Energy transfers Flashcards
Kinetic energy
Energy in moving objects, eg comets, runners and cars
How to find kinetic energy?
Kinetic energy = 0.5 x mass x speed²
Gravitational potential energy
Energy stored in a raised object
How to find gravitational energy?
Mass x gravitational field strength x height
Work done
This tells us the amount of energy transferred from one store to another to move an object
How to calculate work done?
Force (N) x Distance (m)
Power
The amount of energy transferred (or work done) per unit time
How to calculate power?
Energy transferred or work done (J)
——————————————————
Time (s)
Efficiency
A measure of how much energy transferred is used usefully and not dissipated into the surroundings
How to calculate efficiency using power
Useful power output
——————————— x 100
Total power input
How to calculate efficiency using energy transferred?
Useful energy output
——————————— x 100
Total energy input
How can we increase the efficiency?
By reducing wasted energy transfers such as:
Using a lubricant to decrease friction
Using a lid to stop heat being dissipated when using a pan
When heating a pan, place the heating element inside so the heat doesn’t get lost to the base outside it
Use an insulating material such as plastic rather than a conductor such as metal
How can we decrease heat transfers in a building?
Fill the cavity in between the wall with insulating material so heat cant transfer from inside to outside
Use double glazed windows so less energy can pass through
Use loft insulation to reduce heat transfers in a roof
Conduction
Heating by vibrating particles spreading across a material
The kinetic energy in these vibrations causes heat transfers
Convection
When particles with a lot of heat energy in a gas/liquid take the place of particles with little heat energy
How do lava lamps work?
Through convection currents
When heat energy is transferred, the wax’s volume increased
This is because the particles inside move faster and the gaps each between the particles increase causing it to get bigger
The heated wax is less dense than the liquid water so it will rise
It will then cool at the top and become denser, thus sinking
Unit for work done
Joules
Unit of power?
Watts/ W
Unit for work done?
Joules (J)
If someone uses force on an object but it doesn’t move at all has any work been done to the object?
No because the equation is work = force x distance so if there’s no movement, there’s no distance and so no work done
2 types of work done
Mechanical
Electrical
Mechanical work done
Amount of energy transferred to cause an object to move
Electrical work done
Current transferring electrical energy to its components eg electrical energy —> light energy in a lamp
Is convection possible in solids?
No because for convection to take place the particles must be free to move to take the place
